Anode current experiments were carried out to measure the flow of current between the anode and cathode and to determine variations with different anode types and cathode materials. The salinity was also varied to determine effects of different environments. Experiments were attempted on the laboratory experiment but due to the experiment layout with the anode under water results could not be obtained (Table 5.19 and appendix 21). Table 5.19:Anode current experiment results
Anode mAmps (average) mVolts (average)
Used anode 23 (prop) metal tray salinity Freshwater
0.6, 0.1, 0.1 (0.26) 0.010, 0.004, 0.002 (0.004) New hull anode
Metal tray salinity of Freshwater
0.1, 0.1, 0.1 (0.1) 0.001, 0.001, 0.000 (0.0006) New homemade pear anode, metal tray
salinity of Freshwater
0.8, 0.1, 0.2 (0.36) 0.007, 0.002, 0.000 (0.002) New prop anode 1, metal tray salinity of
Freshwater
0.1, 0.5, 0.3 (0.3) 0.000, 0.000, 0.000 New prop anode 2, metal tray salinity
Freshwater
9.6, 10.1, 6 (8.56) 0.522, 0.037, 0.006, 0.001 (0.14)
Used anode 22 (prop), metal tray salinity Freshwater
0.1, 0.1, 0.1 (0.01) 0.02, 0.003, 0.001 (0.008) Used anode 23 (prop) metal tray salinity
Freshwater
0.2, 0.3, 0.01 (0.17) 0.093, 0.000, 0.001 (0.031) New hull anode
Metal tray salinity of 16
43.1, 13.2, 19.4 (25.23) 0.265, 0.086, 0.085 (0.145) New homemade pear anode, metal tray
salinity of 16
3.8, 0.9, 1.2 (1.96) 0.004, 0.003, 0.001 (0.002) New prop anode 1, metal tray salinity of 16 1.8, 3.6, 3.3 (2.9) 0.004, 0.005, 0.001 (0.003) New prop anode 2, metal tray salinity 16 215, 202.7, 101.8 (173) 0.621, 0.324, 0.689 (0.544) Metal shackle (control) 16 0.1, 0.1, 0.1 (0.1) 0.001, 0.001, 0.000 (0.00006) Used anode 22 (prop), metal tray salinity 16 0.004, 0.004, 2.2 (0.736) 0.161, 0.021, 0.175 (0.119) Used anode 23 (prop) metal tray salinity 16 36.4, 9.5, 11.8 (19.23) 0.004, 0.093, 0.007 (0.034) Used anode 22, metal tray salinity 16, metal
sheet
No result with metal sheet added
No result with metal sheet added New hull
Metal tray salinity of 30
8.2, 27.2, 21.4 (18.93) 0.019, 0.004, 0.004 (0.009) New homemade pear anode, metal tray
salinity of 30
0.2, 0.1, 0.1 (0.13) 0.002, 0.001, 0.000 (0.001) New prop anode 1, metal tray salinity of 30 0.1, 0.1, 0.1 (0.1) 0.004, 0.000, 0.001 (0.0016) New prop anode 2, metal tray salinity 30 116.9, 216.5, 211.1 (181.5) 0.422, 0.463, 0.489 (0.458) Metal shackle (control) 30 0.1, 0.1, 0.1 (0.1) 0.000, 0.000, 0.000 Used anode 22 (prop), metal tray salinity 30 16.3, 9.1, 8.5 (11.3) 0.095, 0.001, 0.009 (0.035) Metal shackle (control) 30 0.1 0.0, 0.1 (0.06) 0.004, 0.001 0.013 (0.006)
The current experiments showed mixed results, variation in mAmps and mVolts was observed among different anodes, but it is hard to draw conclusions from this due to the large variation. Very little variation was observed among salinities, apart from freshwater
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where voltage and amps were lower compared with higher values in higher salinity water, again not unexpected. Using a plastic tray and a metal sheet no results could be obtained, as a connection was easily lost.
5.15MAMPEC MODEL
The MAMPEC model was used to predict zinc water levels for marinas in the Hamble estuary and compared to observed zinc levels from water and sediment samples.
Background data was used for water and sediments, water had a background of 7.46µg/l which was a EA freshwater average and sediment varied per site using data collected in this study (Table 5.20 and appendix 32).
The MAMPEC model generally predicted lower zinc concentrations for areas of high boat density, but in areas of lower boat density predicted zinc levels were similar to those observed. On the Hamble all marinas influence one another due to good flushing of marinas. The model does not take into account effects of other nearby marinas on the Hamble, which are likely to affect zinc levels in other marinas. Sediment concentrations generally had lower concentrations after 5-10 years than the current values with
partitioning coefficients (log Kd) of 3, 5, 10 l/g. A log Kd value of 30 l/g did increase the zinc levels within the sediments over the time period modelled. Log Kd values for the Hamble are likely to be between 3-10 l/g, as these provided results similar to those observed on the Hamble, due to less exchange with sediments occurring at these log Kd values. This once again shows the model cannot take into account effects of other marinas and sources in the estuary. Results for enclosed marinas at Hythe and Ocean Village were different with higher zinc water and sediment concentrations predicted (Table 5.20).
160 Table 5.20:MAMPEC model results Hamble
Marina/site Log Kd l/g Average TDZn µg/l Observed TDZn µg/l Sediment background µg/g Sediment 1 year µg/g Sediment 5 year µg/g Sediment 10 year µg/g
Hamble Point Marina 3 7.61 6.86 74.43 73.7 71 67.8 Hamble Point Marina 5 7.3 6.86 74.43 73.9 71.9 69.6 Hamble Point Marina 10 6.62 6.86 74.43 74.3 73.9 73.4 Hamble Point Marina 30 4.83 6.86 74.43 75.4 78.3 81.9 Stone Pier Marina 3 7.41 7.32 122 120 114 107 Stone Pier Marina 5 7.05 7.32 122 121 115 109 Stone Pier Marina 10 6.28 7.32 122 121 117 113 Stone Pier Marina 30 4.38 7.32 122 122 123 123 Mercury Marina 3 7.46 6.69 148 146 138 129 Mercury Marina 5 7.10 6.69 148 146 139 131 Mercury Marina 10 6.33 6.69 148 147 141 135 Mercury Marina 30 4.41 6.69 148 148 147 146 Swanwick Marina 3 7.46 8.69 150.25 148 140 130 Swanwick Marina 5 7.06 8.69 150.25 148 141 132 Swanwick Marina 10 6.38 8.69 150.25 149 143 137 Swanwick Marina 30 4.45 8.69 150.25 150 149 148 Cabin Boatyard 3 7.48 12.3 134 132 125 117 Cabin Boatyard 5 7.12 12.3 134 132 126 119 Cabin Boatyard 10 6.35 12.3 134 133 128 123 Cabin Boatyard 30 4.42 12.3 134 134 134 134 Foulkes Boatyard 3 7.42 13.16 134 132 125 117 Foulkes Boatyard 5 7.16 13.16 134 132 126 119 Foulkes Boatyard 10 6.38 13.16 134 133 128 123 Foulkes Boatyard 30 4.45 13.16 134 134 134 134 Combined marinas 3 7.98 140 138 131 122 Combined marinas 5 7.59 140 138 132 124 Combined marinas 10 6.77 140 139 134 129 Combined marinas 30 4.72 140 140 140 140
No data was available for Hythe marina sediment and water zinc concentrations, so
7.46µg/l was used like on the Hamble for water and a sediment value of 142µg/g observed at Ocean Village Marina, for Ocean village sediment data was available from this study and a background water value of 7.46µg/l was used (Table 5.21).
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Table 5.21:MAMPEC model results Southampton Water
Marina/site Log Kd l/g TDZn µg/l Observed TDZn µg/l Sediment background µg/g Sediment 1 year µg/g Sediment 5 year µg/g (range) Sediment 10 year µg/g (range)
Hythe Marina 3 62.6 No data No data (142) 143 146 149 Hythe Marina 5 57.6 No data No data (142) 144 154 165 Hythe Marina 10 47.8 No data No data (142) 148 169 194 Hythe Marina 30 28.6 No data No data (142) 154 200 253 Ocean Village Marina 3 12 19.22 142 140 133 126 Ocean Village Marina 5 11.4 19.22 142 141 135 129 Ocean Village Marina 10 10.1 19.22 142 141 138 135 Ocean Village Marina 30 7.06 19.22 142 143 147 152
The MAMPEC model tends to under predict total dissolved zinc levels in areas of high boat density and over predict in areas of lower boat density for open marinas. Hythe Marina (enclosed) and Ocean Village (semi enclosed) on Southampton Water and the Itchen showed levels expected for enclosed marinas (Table 5.21). Zinc concentrations within sediments rose in Hythe enclosed marina at all selected log Kd partition
coefficients, the sediments in areas outside of the marina were predicted to have levels significantly lower. Sediment predictions for Ocean village marina showed similar trends to the marinas on the Hamble, with metal concentrations decreasing at most log Kd partition coefficients. The model struggled to predict accurate sediment and water zinc levels at the same time.
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